However, Durban based Aids expert Dr Salim Abdool Karim said this did not mean that a cure has been found.
The British man has become the second known adult worldwide to be “functionally cured” after he received a bone marrow transplant from an HIV-resistant donor.
Almost three years after he received bone marrow stem cells from a donor with a rare genetic mutation that resists HIV infection - and more than 18 months after he came off antiretroviral drugs - highly sensitive tests still show no trace of the man’s previous HIV infection.
“There is no virus there that we can measure. We can’t detect anything,” said Ravindra Gupta, a professor and HIV biologist who co-led a team of doctors treating the man.
The case is proof of the concept that scientists will one day be able to end Aids, and marks a “critical moment” in the search for an HIV cure.
However, Abdool Karim emphasised that, at this stage, there was still no actual cure for the disease.
“Right now we are far from a cure. If anything, this patient from London gives us some clues on how to approach research for a cure,” he said.
He explained that the bone marrow transplant surgery replaces the patient’s HIV-susceptible blood cells with the genetic anomaly in the HIV-resistant donor and would provide more clues to developing a foolproof cure.
Abdool Karim, who is the director of the Centre for the Aids Programme of Research in South Africa (Caprisa), said they were not pursuing the same bone marrow transplant approach in their research.
Instead, Caprisa’s researchers were looking at studies around how antibodies could help in fighting against the virus and clearing it from the body.
“We are undertaking studies in Durban using antibodies to develop a cure approach relevant to patients in Africa. To eventually get a cure, we are going to try many options, many of which will fail, but each study gives us clues toward a cure,” he said.
South Africa has the largest HIV epidemic in the world, with 7.1million people living with the virus.
Gupta described his patient as “functionally cured” and “in remission”, but cautioned: “It’s too early to say he’s cured.”
The man is being called “the London patient”, in part because his case is similar to the first known case of a functional cure of HIV in an American man, Timothy Brown, who became known as “the Berlin patient” when he underwent similar treatment in Germany in 2007 which also cleared his HIV.
Brown, who had been living in Berlin, has since moved to the US and, according to HIV experts, is still HIV-free.
Gupta, now at Cambridge University, treated the London patient when he was working at University College London. The man had contracted HIV in 2003, Gupta said, and in 2012 was also diagnosed with a type of blood cancer called Hodgkin’s lymphoma.
In 2016, when he was sick with cancer, doctors decided to seek a transplant match for him.
“This was really his last chance of survival,” Gupta told Reuters.
The donor - who was unrelated - had a genetic mutation which is known as “CCR5 delta 32”, which confers resistance to HIV.
The transplant went relatively smoothly, Gupta said, but there were some side-effects, including the patient suffering a period of “graft-versus-host” disease - a condition in which donor immune cells attack the recipient’s immune cells.
Most experts say it is inconceivable that such treatments could be a way to cure all patients. The procedure is expensive, complex and risky. To do this in others, exact-match donors would have to be found in the tiny proportion of people - most of them of northern European descent - who have the CCR5 mutation that makes them resistant to the virus.
“Although this is not a viable large-scale strategy for a cure, it does represent a critical moment,” said Anton Pozniak, president of the International Aids Society. “The hope is that this will eventually lead to a safe, cost-effective and easy strategy... using gene technology or antibody techniques.”
Specialists said it is also not yet clear whether the CCR5 resistance is the only key - or whether the graft-versus-host disease may have been just as important. Both the Berlin and London patients had this complication, which may have played a role in the loss of HIV-infected cells, Gupta said.
His team plan to use these findings to explore potential new HIV treatment strategies.